import java.util.LinkedList;
import java.util.Queue;

public class MyStack {

    //用栈实现队列
    // 要用两个栈


    //用队列实现栈
    private Queue<Integer> qu1;
    public Queue<Integer> qu2;
    public MyStack() {
        qu1 = new LinkedList<>();
        qu2 = new LinkedList<>();
    }

    //入栈
    public void push(int x) {
        if(!qu1.isEmpty()){
            qu1.offer(x);
        } else if (!qu2.isEmpty()) {
            qu2.offer(x);
        }else {
            qu1.offer(x);
        }
    }

    public int pop() {
        if (empty()){
            return -1; //两个队列都为空，意味这当前的栈为空
        }
        if(!qu1.isEmpty()){
            int size = qu1.size();
            int val = 0;
            for (int i = 0; i <size -1; i++) {
                val =  qu1.poll();
                qu2.offer(val);
            }
            return qu1.poll();
        } else{
            int size = qu2.size();
            int val = 0;
            for (int i = 0; i < size -1; i++) {
                val =  qu2.poll();
                qu1.offer(val);
            }
            return qu2.poll();
        }
    }

    public int top() {
        if (empty()){
            return -1;
        }
        if(!qu1.isEmpty()){
            int size = qu1.size();
            int val = -1;
            for (int i = 0; i <size; i++) {
                val =  qu1.poll();
                qu2.offer(val);
            }
            return val;
        } else{
            int size = qu2.size();
            int val = -1;
            for (int i = 0; i < size; i++) {
                val =  qu2.poll();
                qu1.offer(val);
            }
            return val;
        }
    }

    public boolean empty() {
        return qu1.isEmpty() && qu2.isEmpty();
    }
}
